Multi-layer co-extruded roofing membrane

Abstract

A multi-layer roofing membrane is provided including a top sheet including a co-extruded cap and inner layer and a bottom sheet. The use of a co-extrusion die allows for multi-layer sheets that reduce the need for expensive fillers in all but a cap layer of the membrane. A scrim reinforcement layer is optionally embedded in the membrane. When installed on a roof substrate, the membrane can be sealed by heat welding the seams of the membrane sheets or by other means.

1. A structural membrane comprising a polymeric top sheet and bottom sheet, wherein said top sheet comprises a co-extruded cap layer, and an upper inner layer oriented between said cap layer and said bottom sheet, said cap layer and said upper inner layer being co-extruded through a common die creating an intimately bonded bi-layer, said cap layer further comprising a thermoplastic olefin, and wherein said bottom sheet comprises a co-extruded lower inner layer and a core layer, said lower inner layer and said core layer being co-extruded through a second die to create an intimately bonded bi-layer. 
     
     
       2. The membrane of  claim 1 , further comprising an intermediate scrim layer positioned between said top and bottom sheets. 
     
     
       3. The membrane of  claim 1 , wherein said core layer comprises a thermoplastic olefin. 
     
     
       4. The membrane of  claim 1 , wherein said cap layer comprises fire retardant additives and said other layers are at least substantially free of such additives. 
     
     
       5. The membrane of  claim 1 , wherein said die is a dual cavity die. 
     
     
       6. The membrane of  claim 1 , wherein said cap layer comprises a fire retardant, and a UV stabilizer. 
     
     
       7. The membrane of  claim 1 , wherein at least one of said layers except said cap layer comprises a reinforcing filler that functions to improve the mechanical properties of said membrane. 
     
     
       8. The membrane of  claim 7 , where said reinforcing tiller comprises wollastonite. 
     
     
       9. The membrane of  claim 1 , wherein said membrane comprises a nano-mineral or nano-clay. 
     
     
       10. The membrane of  claim 1 , wherein said upper inner layer comprises linear low density polyethylene (LLDPE). 
     
     
       11. The membrane of  claim 10 , wherein said inner layer comprises a LLDPE/PP blend. 
     
     
       12. The membrane of  claim 1 , wherein said cap layer comprises a pigment and wherein said other layers are substantially free of pigment. 
     
     
       13. The membrane of  claim 1 , wherein said membrane comprises an extruded adhesive on the edges of said membrane. 
     
     
       14. The membrane of  claim 1 , wherein said cap layer comprises at least one of liquid crystal polymer, a fluoropolymer, or nano-mineral oxide/hydroxide. 
     
     
       15. The membrane of  claim 1 , wherein each of said cap layer, upper inner layer, lower inner layer and core layer has a thickness of from about 5-23 mils (0.13-0.58 mm). 
     
     
       16. The membrane of  claim 15 , where said cap layer has a thickness of about 21 mils (0.53 mm), said upper inner layer has a thickness of about 6 mils (0.15 mm), said lower inner layer has a thickness of about 6 mils (0.15 mm), and said core layer has a thickness of about 21 mils (0.53 mm). 
     
     
       17. The membrane of  claim 2 , wherein said scrim comprises polypropylene, polyethylene terephthalate, and/or polyester. 
     
     
       18. The membrane of  claim 1 , wherein at least one of said layers comprise a blend of a plastomer, low density polyethylene, and a propylene based polymer. 
     
     
       19. The membrane of  claim 1 , wherein said roofing membrane is characterized by having a flexural modulus of from 10,000 to 30,000 psi (69-207 MPa). 
     
     
       20. The membrane of  claim 18 , where the low-density polyethylene includes linear low density polyethylene. 
     
     
       21. The membrane of  claim 20 , where the linear low density polyethylene includes an ethylene-a-olefin copolymer including from about 2.5 to about 13 mole percent mer units deriving from a-olefins. 
     
     
       22. The membrane of  claim 21 , where the linear low density polyethylene is characterized by a density of from about 0.885 g/cc to about 0.930 g/cc per ASTM D-792. 
     
     
       23. The membrane of  claim 18 , where the propylene-based polymer comprises a propylene homopolymer or copolymer comprising propylene and a comonomer, and where the copolymer includes, on a mole basis, a majority of mer units derived from propylene. 
     
     
       24. The membrane of  claim 23 , where the propylene-based copolymers include from about 2 to about 6 mole percent mer units deriving from comonomer, with the balance including mer units deriving from propylene. 
     
     
       25. The membrane of  claim 18 , further comprising a flame retardant selected from the group consisting of halogenated tlame retardants, non-halogenated flame retardants, and mixtures thereof. 
     
     
       26. The membrane of  claim 25 , where the halogenated flame retardants include halogenated hydrocarbons, where the halogenated hydrocarbons include hexabromocyclododecane, N,N′-ethylene-bis-(tetrabromophthalimide), and mixtures thereof, and where the non-halogenated flame retardants include magnesium hydroxide, aluminum trihydrate, zinc borate, ammonium polyphosphate, melamine polyphosphate, and mixtures thereof. 
     
     
       27. The membrane of  claim 26 , where the magnesium hydroxide includes a treated magnesium hydroxide or a functionalized magnesium hydroxide. 
     
     
       28. The membrane of  claim 27 , where the magnesium hydroxide includes magnesium oxide treated with or reacted with a carboxylic acid, or where the magnesium hydroxide includes that treated or reacted with stearic acid, or where the magnesium hydroxide includes that treated or reacted with silicon-containing compounds selected from the group including silanes, and polysiloxanes, or where the magnesium hydroxide includes magnesium hydroxide treated with titanates. 
     
     
       29. The membrane of  claim 18 , where the at least one layer comprises i) from about 5 to about 50% by weight plastomer, ii) from about 10 to about 90% by weight low density polyethylene, and iii) from about 5 to about 50% by weight propylene-based polymer based upon the total weight of the plastomer, low density polyethylene, and propylene-based polymer, and also includes iv) from about 10 to about 50% by weight magnesium hydroxide, based upon the total weight of the at least one layer. 
     
     
       30. The membrane of  claim 29 , where the at least one layer includes i) from about 10 to about 45% by weight plastomer, ii) from about 15 to about 85% by weight low density polyethylene, and iii) from about 10 to about 45% by weight propylene-based polymer based upon the total weight of the plastomer, low density polyethylene, and propylene-based polymer, and also includes iv) from about 15 to about 45% by weight magnesium hydroxide, based upon the total weight of the at least one layer. 
     
     
       31. The membrane of  claim 18 , where the at least one layer includes at least 31% by weight low density polyethylene based upon the total weight of the plastomer, low density polyethylene, and propylene-based polymer. 
     
     
       32. The membrane of  claim 31 , where the at least one layer includes at least 35% by weight low density polyethylene. 
     
     
       33. The membrane of  claim 1 , wherein at least one of said top and bottom sheets comprises at least three distinct layers. 
     
     
       34. The membrane of  claim 1 , wherein said membrane comprises a roofing membrane. 
     
     
       35. The membrane of  claim 1 , wherein said membrane comprises a geo membrane. 
     
     
       36. A structural membrane comprising a polymeric top sheet and bottom sheet and a scrim positioned therebetween, wherein said top sheet comprises a co-extruded cap layer and an upper inner layer, wherein said bottom sheet comprises a co-extruded lower inner layer and a core layer, wherein said cap layer and said upper inner layer are co-extruded through a first die, and wherein said lower inner layer and said core layer are co-extruded through a second die, creating intimately bonded top and bottom bi-layers, said cap and core layers comprising a thermoplastic olefin. 
     
     
       37. The membrane of  claim 36 , wherein said cap layer comprises tire retardant additives and said other layers are at least substantially free of such additives. 
     
     
       38. The membrane of  claim 36 , wherein at least one of said first or second dies is a dual cavity die. 
     
     
       39. The membrane of  claim 36 , wherein said cap layer comprises a fire retardant, and a UV stabilizer. 
     
     
       40. The membrane of  claim 36 , wherein at least one of said layers except said cap layer comprises a reinforcing filler that functions to improve the mechanical properties of said membrane. 
     
     
       41. The membrane of  claim 40 , where said reinforcing filler comprises wollastonite. 
     
     
       42. The membrane of  claim 36 , wherein said membrane comprises a nano-mineral or nano-clay. 
     
     
       43. The membrane of  claim 36 , wherein said upper inner layer comprises linear low density polyethylene (LLDPE). 
     
     
       44. The membrane of  claim 43 , wherein said inner layer comprises a LLDPE/PP blend. 
     
     
       45. The membrane of  claim 36 , wherein said cap layer comprises a pigment and wherein said other layers are substantially free of pigment. 
     
     
       46. The membrane of  claim 36 , wherein said membrane comprises an extruded adhesive on the edges of said membrane. 
     
     
       47. The membrane of  claim 36 , wherein said cap layer comprises at least one of liquid crystal polymer, a fluoropolymer, or nano-mineral oxide/hydroxide. 
     
     
       48. The membrane of  claim 36 , wherein each of said cap layer, upper inner layer, lower inner layer and core layer has a thickness of from about 5-23 mils (0.13-0.58 mm). 
     
     
       49. The membrane of  claim 36 , where said cap layer has a thickness of about 21 mils (0.53 mm), said upper inner layer has a thickness of about 6 mils (0.15 mm), said lower inner layer has a thickness of about 6 mils (0.15 mm), and said core layer has a thickness of about 21 mils (0.53 mm). 
     
     
       50. The membrane of  claim 36 , wherein said scrim comprises polypropylene, polyethylene terephthalate, and/or polyester. 
     
     
       51. The membrane of  claim 36 , wherein at least one of said layers comprise a blend of a plastomer, low density polyethylene, and a propylene based polymer. 
     
     
       52. The membrane of  claim 36 , wherein at one of said cap layer and upper inner layer of said first sheet and at least one of said lower inner layer and core layer of said second sheet has a greater width than a width of said scrim, such that said scrim is completely surrounded by said layers on the sides of the membrane. 
     
     
       53. The membrane of  claim 52 , wherein each of said cap layer, upper inner layer, lower inner layer, and core layer all have a greater width than a width of said scrim. 
     
     
       54. The membrane of  claim 52 , wherein only said cap layer and said core layer have a greater width than a width of said scrim. 
     
     
       55. The membrane of  claim 52 , wherein only said upper and lower inner layers have a greater width than a width of said scrim. 
     
     
       56. The membrane of  claim 36 , wherein said roofing membrane is characterized by having a flexural modulus of from 10,000 to 30,000 psi (69-207 MPa). 
     
     
       57. The membrane of  claim 36 , wherein at least one of said top and bottom sheets comprises at least three distinct layers. 
     
     
       58. The membrane of  claim 36 , wherein said membrane comprises a roofing membrane. 
     
     
       59. The membrane of  claim 36 , wherein said membrane comprises a geo membrane. 
     
     
       60. A structural membrane comprising polymeric top and bottom sheets and an intermediate scrim positioned therebetween, said top sheet comprising a co-extruded cap layer and upper inner layer, and said bottom sheet comprising a co-extruded lower inner layer and core layer, each of said co-extruded layers forming intimately bonded bi-layers, wherein said top and bottom sheets have a greater width than a width of said scrim, such that said scrim is completely surrounded by said sheets on the sides of the membrane. 
     
     
       61. A roof deck having a roofing membrane adhered thereto, said roofing membrane comprising at least a top and bottom sheet bonded together, said top sheet comprising a co-extruded cap layer and upper inner layer, wherein said upper inner layer is oriented between said cap layer and said bottom layer, said cap and upper inner layers being coextruded through a common die creating an intimately bonded bi-layer, said cap layer comprising a thermoplastic olefin and one or more additives that are at least substantially missing from the other layers, and wherein said bottom sheet comprises a co-extruded lower inner layer and core layer, said lower inner layer and said core layer being co-extruded through a second die to create an intimately bonded bi-layer.